set up yaml config for assets

need to set up in this way, see:
spf13/viper#390 (comment)

also, only works for the layout for now, need to get other pages working with this config as well.

when it's local, this also enables static file server.

cmd/web/main.go

@@ -17,10 +17,31 @@ import (
 	"github.com/gorilla/feeds"
 	"github.com/gorilla/mux"
 	"github.com/gosimple/slug"
+	"github.com/pkg/errors"
+	"github.com/spf13/viper"
 	"golang.org/x/net/html"
 	"gopkg.in/yaml.v2"
 )
 
+type Config struct {
+	AssetsUrl    string
+	AssetsPrefix string
+}
+
+func (c Config) IsLocal() bool {
+	return strings.Index(c.AssetsUrl, "/") == 0
+}
+
+func (c Config) FullAssetsUrl() string {
+	if c.AssetsPrefix == "" {
+		return c.AssetsUrl
+	}
+	return fmt.Sprintf("%s/%s",
+		strings.TrimSuffix(c.AssetsUrl, "/"),
+		strings.TrimSuffix(c.AssetsPrefix, "/"),
+	)
+}
+
 type Post struct {
 	Body               template.HTML
 	Images             []string
@@ -66,13 +87,26 @@ func rankByTagCount(tagFrequencies map[string]*Tag) TagCountPairList {
 	return pl
 }
 
+var config Config
+var layoutConfig LayoutConfig
 var tagsList TagCountPairList
 var posts []*Post
 var postsBySlug map[string]*Post
 var postsByTagSlug map[string][]*Post
 var tagsBySlug map[string]*Tag
 
 func main() {
+	var configErr error
+	config, configErr = parseConfig()
+	if configErr != nil {
+		log.Fatal(configErr)
+	}
+
+	layoutConfig = LayoutConfig{
+		AssetsUrl:                 config.FullAssetsUrl(),
+		GoogleAnalyticsTrackingId: os.Getenv("TUGBERKWEB_GoogleAnalytics__TrackingId"),
+	}
+
 	tagsBySlug = make(map[string]*Tag)
 	postsBySlug = make(map[string]*Post)
 	postsByTagSlug = make(map[string][]*Post)
@@ -215,7 +249,9 @@ func main() {
 	})
 
 	fs := http.FileServer(http.Dir("../../web/static"))
-	r.PathPrefix("/assets/").Handler(http.StripPrefix("/assets/", fs))
+	if config.IsLocal() {
+		r.PathPrefix("/assets/").Handler(http.StripPrefix("/assets/", fs))
+	}
 	r.PathPrefix("/content/images/").HandlerFunc(legacyBlogImagesRedirector)
 	r.HandleFunc("/archive/{slug}", blogPostPageHandler)
 	r.HandleFunc("/tags/{tag_slug}", tagsPageHandler)
@@ -237,6 +273,30 @@ func main() {
 	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%s", serverPortStr), CaselessMatcher(r)))
 }
 
+func parseConfig() (Config, error) {
+	viper.SetConfigType("yaml")
+	viper.SetConfigName("config")
+	viper.AddConfigPath("../../")
+	configErr := viper.ReadInConfig()
+	if configErr != nil {
+		return Config{}, fmt.Errorf("Fatal error config file: %s \n", configErr)
+	}
+	var assetsUrl string
+	if viperVal := viper.Get("assets_url"); viperVal == nil {
+		return Config{}, errors.New("Fatal error: 'assets_url' config value doesn't exist")
+	} else {
+		assetsUrl = viperVal.(string)
+	}
+	var assetsPrefix string
+	if viperVal := viper.Get("assets_prefix"); viperVal != nil {
+		assetsPrefix = viperVal.(string)
+	}
+	return Config{
+		AssetsUrl:    assetsUrl,
+		AssetsPrefix: assetsPrefix,
+	}, nil
+}
+
 func CaselessMatcher(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		r.URL.Path = strings.ToLower(r.URL.Path)
@@ -256,6 +316,7 @@ type Layout struct {
 
 type LayoutConfig struct {
 	GoogleAnalyticsTrackingId string
+	AssetsUrl                 string
 }
 
 type Home struct {
@@ -319,7 +380,7 @@ type Page interface {
 }
 
 func speakingPageHandler(w http.ResponseWriter, r *http.Request) {
-	ExecuteTemplate(w, r, []string{
+	ExecuteTemplate(w, r, layoutConfig, []string{
 		"../../web/template/speaking.html",
 		"../../web/template/shared/speaking-activity-card.html",
 	}, SpeakingPage{
@@ -384,7 +445,7 @@ func tagsPageHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	ExecuteTemplate(w, r, []string{
+	ExecuteTemplate(w, r, layoutConfig, []string{
 		"../../web/template/tag.html",
 		"../../web/template/shared/post-item.html",
 	}, TagsPage{
@@ -407,7 +468,7 @@ func blogPostPageHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	ExecuteTemplate(w, r, []string{"../../web/template/post.html"}, PostPage{
+	ExecuteTemplate(w, r, layoutConfig, []string{"../../web/template/post.html"}, PostPage{
 		Post:   post,
 		AdTags: strings.Join(post.Metadata.Tags, ","),
 	})
@@ -421,12 +482,12 @@ func legacyBlogImagesRedirector(w http.ResponseWriter, r *http.Request) {
 
 func staticPage(page string) func(w http.ResponseWriter, r *http.Request) {
 	return func(w http.ResponseWriter, r *http.Request) {
-		ExecuteTemplate(w, r, []string{fmt.Sprintf("../../web/template/%s.html", page)}, nil)
+		ExecuteTemplate(w, r, layoutConfig, []string{fmt.Sprintf("../../web/template/%s.html", page)}, nil)
 	}
 }
 
 func homeHandler(w http.ResponseWriter, r *http.Request) {
-	ExecuteTemplate(w, r, []string{
+	ExecuteTemplate(w, r, layoutConfig, []string{
 		"../../web/template/home.html",
 		"../../web/template/shared/post-item.html",
 		"../../web/template/shared/speaking-activity-card.html",
@@ -437,15 +498,15 @@ func homeHandler(w http.ResponseWriter, r *http.Request) {
 }
 
 func blogHomeHandler(w http.ResponseWriter, r *http.Request) {
-	ExecuteTemplate(w, r, []string{
+	ExecuteTemplate(w, r, layoutConfig, []string{
 		"../../web/template/blog.html",
 		"../../web/template/shared/post-item.html",
 	}, Blog{
 		Posts: posts,
 	})
 }
 
-func ExecuteTemplate(w http.ResponseWriter, r *http.Request, templatePaths []string, data interface{}) {
+func ExecuteTemplate(w http.ResponseWriter, r *http.Request, config LayoutConfig, templatePaths []string, data interface{}) {
 	t := template.New("")
 	t = t.Funcs(template.FuncMap{"mod": func(i, j int) bool { return i%j == 0 }})
 	t, err := t.ParseFiles(append(templatePaths, "../../web/template/layout.html")...)
@@ -485,9 +546,7 @@ func ExecuteTemplate(w http.ResponseWriter, r *http.Request, templatePaths []str
 		Data:        data,
 		Section:     section,
 		AdTags:      adTags,
-		Config: LayoutConfig{
-			GoogleAnalyticsTrackingId: os.Getenv("TUGBERKWEB_GoogleAnalytics__TrackingId"),
-		},
+		Config:      config,
 	}
 	templateErr := t.ExecuteTemplate(w, "layout", pageContext)
 	if templateErr != nil {

config.yaml

@@ -0,0 +1,2 @@
+assets_url: "/assets"
+assets_prefix: ""

go.mod

@@ -7,6 +7,8 @@ require (
 	github.com/gorilla/feeds v1.1.1
 	github.com/gorilla/mux v1.7.4
 	github.com/gosimple/slug v1.9.0
+	github.com/pkg/errors v0.8.1
+	github.com/spf13/viper v1.7.1
 	golang.org/x/net v0.0.0-20200506145744-7e3656a0809f
 	gopkg.in/yaml.v2 v2.2.8
 )